The present invention relates to a power supply for an ozone generator and more particularly, to a power supply which is applicable to generators using tubular electrodes.
Industrial generators of this type are usually composed of a set of elementary generators connected in parallel within the same enclosure, each generator comprising two conducting electrodes separated by a narrow gap through which gas is passed and a dielectric material, usually glass.
These electrodes are concentric. Inside an outer metal electrode, around which cooling water circulates, a glass tube is placed. The tube is closed at one end and metallized internally, said metallization constituting the second electrode. A 2-3 mm discharge gap is provided between the glass tube and the metal tube through which is passed either pure oxygen or a gaseous mixture, such as atmospheric air containing oxygen.
Between these two electrodes, a growing alternating potential difference is applied and from a specified value of the voltage across the terminals of the generator corresponding to the breakdown voltage of the gas there appears in the discharge gap a violet corona, resulting in the partial conversion of oxygen into ozone.
The ozone production by such a generator is a growing function of the electrical power applied thereto and the control of this production at the required value is therefore effected by adjusting said power. This adjustment is effected by modifying the value of the primary voltage of the transformer so as to obtain in the secondary a voltage applied to the generator varying between 6 and 8 kV, the value of the breakdown voltage is around 18 kV at 50 Hz. This voltage is usually varied by means of an autotransformer having sliding contacts and placed in the primary circuit of the transformer. The power applied to an elementary generator can thus be varied, for example, between 0 and 400 watts, by moving the sliding contacts of the autotransformer.
From the electrical point of view, an ozone generator is a capacitive load, its power factor being on the order of 0.5, and to provide 400 watts of power, an apparent power of approximately 800 voltamperes must therefore be applied. For large-production apparatus consisting of a large number of generators in parallel, this apparent power can attain several hundreds of kVA, on the order of 500 kVA for a 600 generator apparatus. To prevent a high reactive power from being reflected to the low-voltage supply network of the transformer of the generator, an inductor designed to compensate for the capacitive charge of the generator is usually provided in the primary of this transformer according to the following equation (C stands for the capacitance of the generator, L the value of the inductance, f the frequency of the alternating current): EQU (2.pi.f).sup.2 LC=1
The presence of this inductor also enables one to limit the value of the current in the event of a short circuit in the ozone generator. In this case, in the absence of an inductor, the value of the current is only limited by the ideal impedance of the transformer and can thus attain more than twenty times its normal value, causing considerable damage to the generator. In the event of a short circuit, the voltage drop caused by the inductor automatically limits the current to an acceptable value.
However, this prior art power supply for an ozone generator has a number of drawbacks. In fact, it makes use of several electromagnetic elements having a considerable weight and occupying a great deal of space. In particular, the transformer must be designed not for the active power consumed by the generator, but for the required apparent power. Thus, it is necessary to use an autotransformer with complex mechanical control elements and without a high degree of operating reliability. It is also relatively expensive.